You know, that's the weird thing. I have a harder time with the early stages (although its not as bad now as in the 3DS version, since more people in the fights means more people taking each other out and using items on others instead of me) than i do with Master Core's boss fight. It might just be i've learned the pattern now, which is why im so good, but i don't struggle on any of the forms anymore, except Lizard a bit, since i might not be able to react to his attack when he goes in and out from the background because i was pulling off a laggy attack to do alot of damage.
Even Master Blades is easy really, when he holds the largest sword up for a couple seconds, the best thing to do is just run to the other side of the stage while he's preparing it, and just shield. He attacks while he moves during this part, and he'll waste some of his attack moving to you, most of the time he'll only get enough time to land the final hits on you, and if you're shielding you'll be safe.
I really wanna try doing this with Lucario now though, if only to see how i'd do, with how much damage i'm gonna take.